J Korean Ophthalmol Soc.  2013 Feb;54(2):199-209. 10.3341/jkos.2013.54.2.199.

Anterior Elevation Changes Following Corneal Crosslinking for Keratoconus

• Yang JH
• Jin KH

• KMID: 2216653
• DOI: http://doi.org/10.3341/jkos.2013.54.2.199

Abstract

PURPOSE
To report the results according to anterior elevation changes following corneal crosslinking (CXL) treatment for keratoconus.
METHODS
The present retrospective study included 14 patients (15 eyes) with progressive keratoconus who underwent CXL with a follow-up of 12 months. Patients were classified into 2 groups according to pre and postoperative anterior elevation difference maps. On the preoperative anterior elevation map, distances from maximum anterior elevation to pupil center were compared between the 2 groups. The outcome of best correct visual acuity (BCVA), maximum keratometry and parameters of corneal topography were compared between the 2 groups before CXL as well as 6 and 12 months after CXL.
RESULTS
The anterior elevation changes were classified as group 1 (-7.88 +/- 10.53 micrometer) or group 2 (8.71 +/- 5.99 micrometer) (p = 0.001). The preoperative corneal topography of eyes observed in group 1 (0.19 +/- 0.13 mm) had shorter mean distances from maximum anterior elevation to pupil center than eyes in group 2 (0.47 +/- 0.23 mm) (p = 0.018). BCVA (log MAR) improved from 0.68 +/- 0.78 to 0.57 +/- 0.81 (p = 0.115) 12 months after CXL in group 1 and decreased from 0.51 +/- 0.34 to 0.56 +/- 0.38 (p = 0.109) 12 months after CXL in group 2. The maximum keratometry decreased from 63.01 +/- 19.07D to 58.95 +/- 16.32D (p = 0.017) in group 1 and increased from 60.70 +/- 9.46D to 61.29 +/- 7.51D (p = 0.674) in group 2.
CONCLUSIONS
Clinical and optical effects improved postoperatively in group 1, and were stabilized in group 2. The preoperative distance from maximum anterior elevation to pupil center and the anterior elevation changes after CXL were factors in predicting the CXL outcome.

Keyword

Anterior elevation changes; Corneal crosslinking; Keratoconus

MeSH Terms

Corneal Topography
Eye
Follow-Up Studies
Glycolates
Humans
Keratoconus
Pupil
Retrospective Studies
Visual Acuity
Glycolates

Figure

• 

  Figure 1. The anterior elevation map in topography of Pentacam in keratoconus patients. (A) Anterior elevation from best fit sphere (BFS) at preoperative period. (B) Anterior elevation from BFS at postoperative 6 months. (C) Anterior elevation form BFS at postoperative 12 months. (D) Anterior elevation (12 months after CXL to preoperative) difference maps. (E) Color bar showing the elevation scale as gradation of the color scale. If the area of the cornea shows red color, examination results show highest area in the cornea.

• 

  Figure 2. (A) Anterior chamber analysis of Pentacam showed location of the pupil center (a, b) and the apex of the cornea (0, especially. (B) The 2 Cartesian coordinates was performed after converting (a, b) of the pupil center into (0, 0). That is, (-a, -b) correspond to the corneal apex and (0, 0) correspond to the pupil center; D is distance between the pupil center and the apex of the cornea.

• 

  Figure 3. Anterior elevation (12 months after CXL to preoperative) difference maps in eight eyes. Difference map showed para-central steepening, no change or flattening centrally in group 1.

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  Figure 4. Anterior elevation (12 months after CXL to preoperative) difference maps in seven eyes. Difference map showed para-central flattening with central steepening in group 2.

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  Figure 5. Scatter graphs showed the location of the apex of the cornea and pupil center and represented by the 2-dimensional vector (X,Y); (A) Location of the apex of the cornea showed cluster of points gathered around the inferior part of zero point at preoperative (red circle), postoperative 6 months (navy triangle) and 12 months (yellow quadrangle) in group 1. (B) Location of the apex of the cornea showed diffuse distributed points around the inferior part of zero points at pre-operative, and location of points moved to zero point in group 2.

• 

  Figure 6. Box and whisker plot represents the mean changes in variables from the baseline at 6 and 12 months. The bottom and the top of the box shows the 25th and 75th percentile and the band near the middle of the box shows median values. A shows mean change in best-corrected visual acuity (BCVA) between baseline and 6, 12 months for group 1 and groups 2. B shows mean change in maximum keratometry values (Kmax) between baseline and 6, 12 months. C shows mean change in mean keratometry values (Kmean) between baseline and 6, 12 months. D shows mean change in spherical equivalent values (SE) between baseline and 6, 12 months. E shows mean change in central corneal thickness (CCT) between baseline and 6, 12 months. F shows mean change in index of surface variance (ISV) between baseline and 6, 12 months. G shows mean change in index of vertical asymmetry (IVA) between baseline and 6, 12 months. *Significantly different between Group 1 and Group 2 (p < 0.05, Mann-Whitney U test). †Significantly different from baseline measurement (p < 0.05, Wilcoxon signed-ranks test).

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  Figure 7. Schematic diagrams of a proposed biochemical model response to corneal crosslinking (CXL). Group 1 (Distance between corneal apex (red triangle) and center (blue circle) is within 0.3 mm); (A) Shrinkage of the surrounding collagen fibrils (violet arrow) lead to equal force due to roughly equal length in all corresponding hemimeridians around the cone apex (black circle represents cross-linked zone); (C) This would result in no significant change or finely pulling up of the cone apex to corneal center (blue dot line) after CXL. There was flattening of corneal center corresponding to corneal apex due to arch shortening effect after CXL. Group 2 (Distance between cor-neal apex and center is far more 0.3 mm); (B) Shrinkage of the collagen fibrils (violet arrow) on one side of a meridian to the displaced cone apex lead to more shrinkage force due to more length than that of the opposite side; (D) This would result in marked pulling up of the cone apex to corneal center after CXL. There was steepening of the corneal center corresponding to peri-apexial area due to arch shortening effect after CXL.

Reference

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